Blitz:
DELETE DELETE DELETE!!!!
Do NOT open them, just delete them!!!!
Madjack:
It sounds like you've been spoofed!!!
You do NOT have the actual virus, but you're getting bounced!!! You want to prevent the bounces landing in your 'inbox', so you need create a rule in Outlook to filter out anything that has the subject line "Returned mail: User unknown". If you're using Hotmail to get your email, you can actually get the email in Outlook Express and create that filter in there. Then the bounces can be sent directly to the trash.
Try this:
Launch Outlook Express.
Then click on tools > accounts > add > mail >
and then just follow the prompts.
You will be prompted for your account, password, etc. Once that's set up and you're sending/receiving just fine.
Then you go to:
Tools > message rules > mail >
then filter based on whatever all of those messages your getting have in common (all of the ones you have been getting have that same subject line.)